PROJECT SUMMARY/ABSTRACT The long-term objectives of the proposed project are to determine the role of the gut microbiome in multiple sclerosis (MS), as well as to develop dietary and gut microbiome-based therapeutic strategies for this disease. MS is a chronic autoimmune disease targeting the central nervous system. It affects 2.5 million people worldwide with significant personal and socioeconomic burdens. Current treatments are usually inadequate; thus there is a need for new therapeutic approaches. One potential therapeutic strategy is dietary manipulation. Preliminary studies show that intermittent fasting confers protection to experimental autoimmune encephalomyelitis (EAE), a murine model for MS, but the underlying mechanisms of protection are unknown. Microbial analysis revealed beneficial changes in the gut microbiome including increased bacteria diversity and increased levels of immuno-modulatory bacteria that could dampen the autoimmune response. In addition, changes in microbial metabolites could contribute to a reduction in autoimmunity. Our preliminary studies revealed that mice undergoing intermittent fasting produced less fecal acetate, a short-chain fatty acid that was reported to increase the production of a pro-inflammatory adipokine (leptin) in a G protein-coupled receptor 41- dependent manner. Importantly, the protective effects associated with the altered microbiome could be transferred from fasting mice to non-fasting mice through fecal microbial transplants. In a pilot trial we just concluded, intermittent fasting in MS patients induced changes in the gut flora and leptin levels recapitulating what we observed in mice with EAE. The proposed studies will delineate the potential pathways by which changes in the gut microbiome caused by intermittent fasting protect against EAE. Aim 1 will determine how the gut microbiome modulates local gut immunity and subsequently influences systemic immune responses, using whole stool transplants from fasting mice to non-fasting mice. The specific protective microbial species will be identified by isolating the over-represented taxa from intermittently fasting mice and testing their ability to modulate the local and systemic immune responses. Aim 2 will test the idea that the gut microbiome protects against EAE by altering leptin and adiponectin production through known pathways controlling their induction. The study will increase knowledge of the mechanisms in dietary-mediated regulation of EAE/MS pathogenesis, thereby laying the groundwork for development of novel therapeutic strategies for MS, including manipulation of the gut microbiome with probiotics and/or prebiotics.